The present invention relates to a pump for circulating water, more specifically to a pump for circulating water which prevents the rise of an impeller by an inner pressure generated when the pump for circulating water operates, secures smooth flow of fluid by preventing the impeller from being affected by an air pressure generated while discharging, to a fluid outlet, part of the fluid and air intruding into the lower part of a pump chamber, thereby allowing smooth rotation of the impeller, and improves durability by preventing damage of the impeller.
In general, pumps for circulating water used as feed water pumps of low pressure boilers use centrifugal pumps, and these pumps are disclosed in prior art, Korean Patent No. 10-1204344. Said patent provides a technology of rotating an impeller installed with a rotor by the electromagnetic induction between a stator and the rotor to introduce fluid (water) to the inlet of a lower part of the reservoir, discharging the fluid (water) through a pathway between a wing piece of an impeller body and an upper cover of the impeller by pumping, and delivering the introduced fluid along a discharge line via an outlet to a place of use such as a heating mat, etc. through a connecting line after heating the fluid by a heating means.
In particular, in the prior art, a plurality of discharge holes vertically penetrating the impeller to be interconnected with the flow pathway are formed so that the fluid in the flow pathway formed between an outer surface of the impeller body and an impeller receiving groove of the inner housing is discharged upwards.
Therefore, according to the prior art, during the pumping action of the impeller, part of the water (part of the fluid) discharged through the pathway between the wing piece and the impeller upper cover and air included therein are smoothly discharged upwards while being introduced into the flow pathway formed between the outer surface of the impeller body and the impeller receiving groove of the inner housing and the discharge holes vertically penetratingly formed through the impeller body. Thus, since cavitation does not occur in the flow pathway even during high speed rotation of the impeller, water is circulated smoothly. Also, since the rise of the impeller is prevented, the vibration or noise can be blocked which is generated from the contact with the inner surface of the upper housing or adjacent parts because of the rise of the impeller.
However, part of water and air introduced into the flow pathway rises through the plurality of discharge holes which vertically penetrate the impeller during the driving of the impeller and are discharged through the wing piece of the impeller. Thus, the pressure of part of water rising along the discharge holes is applied to the wing piece of the impeller, thereby causing a great difference in pressure between the front and the back of the wing piece of the impeller during high speed rotation. Accordingly, the action bothering the rotation may occur, which blocks the rotation of the wing piece of the impeller.
Therefore, there are problems such that the fluid does not flow smoothly because of reduction of a rotating force of the impeller, and that the durability of the impeller is greatly lowered because of damage to the wing piece of the impeller caused thereby as well as generation of noise and excessive vibration.